That is interesting. How much material does the book suggest removing? I had thinned 2 springs in that manor and had issues with both, with one of them actually breaking. I have a feeling I may have removed too much material too quickly causing the problems. That was when I consulted a smith I have used for years who suggested thinning the spring from the sides. I haven't had any issues yet with it, but I also didn't allow the spring to get too hot.
I did this bullet trick on a gun with a lightened trigger, and wow. I have a couple of extra springs around and would like to try thinning them as you described.
I have been staring at the two pictures you have posted for a while now. The first gun appears to have had the lower leg thinned in the center; however, the spring in the second picture does not have the same work done to it. It looks as though the second spring was thinned near the tip. Am I correct or have I been staring at this screen too damn long?